Generally, a relay station (hereinafter abbreviated RS) is proposed for the purpose of cell coverage extension and throughput increase of a mobile communication system. IEEE 802.16e/16m terminal is supported for the relay station. And, this relay station is an active repeater including network entry, mobility, RRM and security functions of a PMP based relay station partially provided with functions of a base station. The relay station decodes a signal received from a transmitting end, re-encodes the decoded signal, and then delivers the re-encoded signal to a receiving end. Therefore, the relay station is able to play a role as a digital amplifier capable of obtaining high performance using noise removal and higher data rate coding. Yet, it is disadvantageous in that the communication via the relay station may generate a delay in the process of decoding and encoding. Moreover, a problem of backward compatibility of PMP mode should be taken into consideration for the communication via the relay station.
A type of a relay station can be categorized in the following manner. First of all, a fixed relay station (RS) is permanently fixed and used for a shade area or a cell coverage increase. This type is usable for a simple repeater. Secondly, a nomadic relay station (RS) is the relay station that can be temporarily installed if the number of users is abruptly incremented. And, the nomadic relay station is the relay station that can be arbitrarily moved within a building. Thirdly, a mobile relay station (RS) is the relay station that can be attached to a public transportation such as a bus, a subway and the like.
FIG. 1 is a diagram of a frame structure for supporting a relay station in a broadband wireless access system according to a related art.
A frame structure shown in FIG. 1 assumes a case that there are two hops between a base station and a relay station. A downlink relay zone (Relay DL Zone) and an uplink relay zone (Relay UL Zone) of a relay station are established within a frame. Data transmitted to a relay station by a base station is allocated as a burst in a downlink of a frame. And, data transmitted to a mobile terminal or an adjacent relay station by a relay station is allocated to a downlink zone of the relay station.
If there is data to be transmitted to a relay station by a mobile terminal or an adjacent relay station, the data is transmitted via a zone allocated to an adjacent relay station or each terminal in an uplink zone of the relay station. The relay station receives the data in the zone allocated to the corresponding relay station in uplink.
FIG. 2 is a diagram for an example of a multi-hop relay to which the present invention is applied.
In a mobile communication system according to a related art, when communication is performed between a base station and a mobile terminal via several relay stations, an interval for a subordinate relay station (RS) or a terminal to receive/transmit data is differently determined according to whether a hop between the base station and the relay station corresponds to an order of an odd number (2n+1, where n is a zero or natural number) or an order of an even number (2n+2). In particular, if a mobile station MS1 receives data from an odd ordered relay station RS1, data is allocated to a downlink access zone. And, another mobile station MS2 in the course of communication with an even ordered relay station RS2 receives data via a downlink relay zone.
FIG. 3 is a diagram for a case that a mobile station receives data via relay stations RS3, RS2 and RS1 to communicate with a serving base station (SBS).
Referring to FIG. 3, in case of a mobile station MS1 receiving data from an odd ordered relay station RS1, it receives data via a downlink access zone of the relay station RS1. In FIG. 3, another mobile station MS2 in the course of communication with an even ordered relay station RS2 receives data via a downlink relay zone of the relay station RS2.
A base station transmits data to a third relay station RS3 via a relay zone. The third relay station RS3 having received the data transmits the corresponding data to the second relay station RS2 via a next frame access zone. The second relay station RS2 receives the data via the access zone and then transmits the corresponding data to the mobile station (e.g., MS2) or the first relay station RS1 via a relay zone of a next subframe. If the first relay station RS1 is further included to the path between the base station and the mobile station (e.g., MS1), the first relay station RS1 receives the data from a relay zone of the second relay station RS2 and then transmits the data to the mobile station via an access zone of a next frame.